Driving device for a centrifugal separator

ABSTRACT

In a centrifugal separator a centrifugal rotor is connected to a vertical spindle, which is supported by a frame and journalled in a first bearing and a second bearing. The centrifugal separator is drivable by an electric motor, the stator of the motor being fixed to the frame such that it is radially immovable relative to it, whereas the rotor of the motor is radially movable together with the spindle. The gap between the rotor and the stator of the motor is dimensioned so that it permits the radial movability of the rotor.

FIELD OF THE INVENTION

The present invention relates to a driving device for a centrifugalseparator, more closely a centrifugal separator comprising

-   -   a centrifugal rotor, which is rotatable about a substantially        vertical rotational axis,    -   a spindle, which extends vertically and at its one end supports        the centrifugal rotor,    -   a frame, which rotatably supports the spindle during normal        operation of the centrifugal rotor by means of a first bearing        and a second bearing, said first bearing being arranged between        the centrifugal rotor and said second bearing,    -   a driving device having an electric motor, which is arranged to        drive the spindle and which comprises a stator, which is        non-rotatably connected to the frame, and a rotor, which is        supported by the spindle between said two bearings,    -   a spring device arranged to permit but counteract by spring        force, in an area axially between the electric motor and the        centrifugal rotor, radial movement of said first bearing        relative to the frame, and    -   a bearing support member supported by the frame and arranged to        prevent substantial radial movement of said second bearing.

BACKGROUND OF THE INVENTION

A centrifugal separator of this kind is described in DE 37 14 627. Thecentrifugal rotor in this case is supported at the top of the verticalspindle, and the driving device comprises an electric standard typemotor, which may be arranged in two different ways.

According to a main alternative the electric motor is situated belowsaid second bearing, as shown in the drawing. Also another alternativeis suggested, in which the electric standard type motor would bearranged between said two bearings. An arrangement according to thelast-mentioned alternative would have the advantage that the wholecentrifugal separator became more compact.

As can be seen from DE 37 14 327 said second (lower) bearing is radiallyimmovable in relation to the frame, whereas said first (upper) bearingmay move somewhat radially, so that the spindle may adapt itself tochanges of position of the centre of gravity of the centrifugal rotor,which occur during operation of the centrifugal rotor. Such changes ofposition always occur to a larger or smaller extent and are caused byunbalance of the centrifugal rotor. Thus, the spindle will alwaysperform oscillatory motions.

An arrangement of an electric standard type motor between the twolayers, in accordance with the proposal in DE 37 14 627, for obtainmentof a more compact centrifugal separator would, however, bring thedisadvantage that the motor were forced to follow said oscillatorymotions of the spindle. This would lead to an increased load on both thebearings and the frame, and particularly in connection with large andheavy centrifugal rotors having correspondingly large and heavy drivingmotors, this could become an unacceptable problem.

The object of the present invention is to provide a driving device for acentrifugal separator of the above defined kind, which driving devicedoes not cause the bearings and the housing being subjected tounacceptably heavy loads but, despite this, makes possible a compactconstruction for the whole centrifugal separator.

SUMMARY OF THE INVENTION

According to the invention, the above-described object may be obtainedby means of a driving device characterized in that the stator of themotor is fixed to the frame in a way such that it is radially immovablerelative to the frame. On the other hand, the rotor of the motor isradially movable relative to the stator of the motor together with thespindle. A gap is defined between the rotor and the stator and is sizedto permit radial movement of the motor rotor.

The invention may, if desired, be used in a centrifugal separator,wherein the spindle is suspended in a frame and the centrifugal rotor issupported at the lower end of the spindle. However, in a preferredembodiment of the invention the centrifugal rotor is supported at theupper end of the spindle.

The present invention prevents spindle oscillating, developed as aconsequence of the centrifugal rotor being unbalanced from beingtransferred to the stator of the electric motor. Therefore, the bearingsof the centrifugal separator are not subjected to unnecessary load as aconsequence of such oscillations. This is despite the fact that theelectric motor as a whole is arranged in the space between the twobearings.

A centrifugal separator of the above-described can kind can include acentrifugal rotor which may weigh up to 1000 kg, or more, and generallyalso includes a lubricating device arranged to provide lubrication tothe two bearings. A preferred embodiment of the driving device accordingto the invention includes a lubricating device that has a generatingmember to generate an oil mist in an oil chamber. The first bearing andthe second bearing are arranged in a first bearing chamber and a secondbearing chamber, respectively. The bearing chambers communicate throughoil passages with the oil chamber. The gap between the rotor and thestator of the motor forms a substantial part of a flow path for oilaxially through the motor.

By this arrangement the oil used for lubrication of the bearings alsomay be used for continuous cooling of the electric motor upon, passagethrough gap between the rotor and the stator of the motor.

Preferably, a fan device is connected to the spindle and is arranged to,transport the oil mist in a circuit that include the gap in the motor.The fan device may be arranged between the first bearing chamber and anintermediate chamber communicating with the gap, the fan device beingarranged to transport oil mist in one of the directions between thefirst bearing chamber and the intermediate chamber.

Preferably, the circuit comprises in addition to the gap in the motor atleast one further passage connecting the bearing chambers with eachother. The passage may be provided in an inexpensive and simple way bybeing created between the outside of the frame and a member connected tothe frame. The passage preferably comprises several channels evenlydistributed around the spindle and delimited between the frame and themember.

For removal of surplus heat, above all from the electric motor, theframe preferably is surrounded by a jacket delimiting a space forthrough flow of a cooling medium in heat transferring contact with theframe. In a preferred embodiment said jacket is double-walled, the innerone of the jacket walls delimiting together with the frame said channelsfor oil mist.

In a centrifugal separator of the kind here in question the spindle isoften dimensioned so that it can be permitted to bend somewhat, even ifinsignificantly, during rotation of the centrifugal rotor. Such bendingmay cause a problem in an arrangement according to the invention, if therotor of the electric motor is not as flexible as the spindle. The rotorof the motor may be composed of stacked ring-shaped discs permanentlyconnected to each other to a very stiff cylindrical body. Even a slightdisplacement of these ring-shaped discs relative to each other duringthe manufacture of the cylindrical body may result in the openings atthe ends of the body not being placed exactly coaxially. Upon mountingof the cylindrical body on the spindle this may lead to the spindlebecoming loaded radially by the body and being brought to deflect froman exactly vertical line. To avoid problems of this kind it is suggestedthat the rotor of the motor at its one end is connected with the spindlein such a way that, in this area, it is radially immovable relative tothe spindle but the remainder is free to move somewhat radially relativeto the spindle, so that the relatively flexible spindle is notunnecessarily loaded by the relatively stiff rotor. Hereby it is alsoavoided that the rotor is damaged upon bending of the spindle duringrotation of the centrifugal rotor. Furthermore, there is no need forvery tight tolerances during the manufacture of the cylindrical body,which is to be the rotor of the electrical motor.

To facilitate connection of the rotor with the spindle in the waydefined above the rotor may comprise a first part in the form of asubstantially cylindrical sleeve and a second part surrounding thesleeve and connected thereto. The second part of the rotor may beconstituted by a body comprising ring-shaped discs of the kind earlierdescribed.

To minimize thermal influence on the spindle from the electric motor therotor is suitably arranged so that a heat-insulating gap is formedbetween the rotor and the spindle at least along a part of the rotor ofthe motor. Such a gap is effective even if it is very thin, e.g. 1 mm.

A driving device according to the invention can be used in a centrifugalseparator, wherein the centrifugal rotor is supported at the upper endof the spindle and the frame surrounds a space, in which the electricmotor and a part of the spindle and also said two bearings are arranged.In such an arrangement the frame may be formed such, namely, that saidspace is completely closed from connection with the surroundingatmosphere below said first bearing. In this manner, it is possible toprovide oil mist lubrication to the bearings without a risk of oil mistleaking out to the surrounding atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in the following with reference to theaccompanying drawing, in which;

FIG. 1 shows an axial section of a driving device for the rotation of acentrifugal rotor,

FIG. 2 shows a cross section through the driving device along the lineII-II in FIG. 1, and

FIG. 3 shows a part of the driving device in a larger scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a part of a centrifugal rotor 1 and a driving device 2 forrotation of the centrifugal rotor around a vertical rotational axis R.The centrifugal rotor 1 is connected to the driving device 2 by means ofa spindle 3.

The driving device 2 comprises a frame, the main part of which consistsof a substantially cylindrical housing 4. This housing supports thespindle 3 via a lower bearing 5 and an upper bearing 6. The lowerbearing 5 is supported by a bearing support member 7, which is connectedwith a bottom plate 8. The bottom plate 8 in turn is connected to thehousing 4. The upper bearing 6 is supported by the upper part of thehousing in a way that is described later.

The upper part of the housing is covered by a cap 9. Immediately belowthe upper bearing 6 a partition 10 is located, which between itself andthe cap 9 delimits an upper chamber 11 in the upper part of the housing4. The upper bearing 6 is situated within the upper chamber 11.

The upper bearing 6 is an angular contact ball bearing, which isdimensioned for transferring substantially all axial forces generatedbetween the spindle 3 and the housing 4. The lower bearing 5, also aball bearing, is dimensioned for transferring substantially only radialforces and is formed to permit some inclination of the spindle 3 inrelation to a vertical line.

An electric motor 12 is arranged between the partition 10 and the bottomplate 8. An intermediate chamber 13 is delimited between the partition10 and the motor 12. The motor 12 comprises a stator 14 and a rotor 15.The stator is rigidly connected to the housing 4, whereas the rotor 15is connected to the spindle and thus rotatable together with the same.Between the stator 14 and the rotor 15, a gap 16 is formed, connectingthe intermediate chamber 13 with a lower chamber 17 formed between themotor 12 and the bottom plate 8. The gap 16 permits a radial movement ofthe spindle 3 and the rotor 15 relative to the stator 14 and the housing4.

The rotor 15 comprises two main parts, a sleeve 18 and a rotor package19. The rotor package 19 consists of moulded ring-shaped metal discswhich, stacked onto each other, surround and are rigidly connected toeach other and to the sleeve 18. The sleeve 18 in turn, at its upperend, is connected to the spindle 3 in a way described in more detailbelow and more clearly shown in FIG. 3.

Along the sleeve 18 there is formed between this and the spindle 3 a gap20 forming a heat-insulating layer, which minimizes thermal influence onthe spindle 3 from the motor 12.

At its upper end the bearing support member 7 supports the lower bearing5. Below the lower bearing 5 the bearing support member 7 delimits anoil chamber 21, which like the lower chamber 17 is partly filled withlubricating oil. The upper free surface of the oil is indicated by asmall triangle. The oil chamber 21 communicates with the lower chamber17 both below the oil surface of the oil through holes 22 and above theoil surface through holes 23 and 24. At its lower part, inside thebearing support member 7, the spindle 3 supports an oil mist generatingmember 25.

Within the upper chamber 11 the upper bearing 6 is supported by thehousing 4 by means of a resilient suspension device comprising bothlower and upper rubber bushings 26 and 27, respectively, and a lower andan upper ring-shaped member 28 and 29, respectively. The lower rubberbushings 26, distributed around the rotational axis R, are arrangedbetween the lower ring-shaped member 28 and the partition 10. The upperrubber bushings 27, also distributed around the rotational axis R, arearranged between the upper ring-shaped member 29 and the cap 9. Thering-shaped members 28, 29 are arranged between the bearing 6 andrespective bushings 26,27. Inside the lower bushings 26, screw springs30 are arranged to make the entire suspension device somewhat stiffer.In the upper ring-shaped member 29 there are radial channels 31connecting the upper chamber 11 with the interior of the bearing 6.

The purpose of the suspension device is to counteract by spring force,in an area axially between the electric motor 12 and the centrifugalrotor 1, a radial movement of the spindle 3 relative to the housing 4.The housing 4 is surrounded by a jacket 32. The jacket has an inner wall33 and an outer wall 34. Between the walls 33,34 a space 35 is formedwhere a cooling fluid, e.g. water, may flow. The cooling fluid in thisway may cool the housing 4, which is heated substantially by theelectric motor during operation of the centrifugal rotor.

The outside of the surrounding wall of the housing 4 is provided withaxial grooves evenly distributed around the rotational axis R. Thesegrooves are covered radially outwardly by the inner wall 33 of thejacket and form channels 36. Each channel 36 communicates at its lowerend with the lower chamber 17 through an opening 37, and communicates atits upper end with the upper chamber 11 through an opening 38.

In the intermediate chamber 13 the spindle 3 supports a fan device 39.This comprises a fan wheel with a number of wings or blades distributedaround the spindle and extending outwards from it. The fan device hasits suction side in communication with the upper chamber 11 through acentral annular passage 40 and its pressure side in communication withthe intermediate chamber 13. Alternatively, the fan device may be turnedin a way having its suction side in communication with the intermediatechamber 13 and its pressure side in communication with the upper chamber11.

The electric motor 12 is connected for its operation to a control unit41. This in turn is connected to a source of current (not shown) andcontains control equipment of some suitable kind for driving of, amongother things, the motor 12. Cables 42 extend between the control unit 41and the stator 14 of the motor through a pipe 43 and an opening 44 inthe housing 4. For shielding off the interior of the control unit 41from the interior of the housing 4, the pipe 43 at its connection to thecontrol unit 41 is provided with a cover or the like, which fills orcovers the interior of the pipe but through which the cables 42 extend.

FIG. 3 shows a part of the driving device according to the invention ina larger scale. Moreover, FIG. 3 illustrates how the aforementionedsleeve 18 at its upper end is connected with the spindle 3.

Thus, as can be seen from FIG. 3, the sleeve 18 has an enlarged portion45 at its upper end. This portion 45 has at least one axial slit 46extending from the upper end of the sleeve 18 and a distance downwards.A screw 47, bridging the slit 46, is arranged to squeeze the portion 45of the sleeve 18 firmly to the spindle 3. Preferably, there are twoslits 46 and two screws 47 arranged diametrically on opposite sides ofthe spindle 3.

The above described driving device operates as follows upon rotation ofthe centrifugal rotor.

By means of the electric motor 12 the spindle 3, and thereby also thecentrifugal rotor 1, is brought into rotation around the rotational axisR. The oil mist generating member 25 thereby is brought to rotate in thelubricating oil present in the oil chamber 21, so that a part of thelubricating oil is transformed into oil mist. The oil mist passesthrough the holes 23,24 and fills the lower chamber 17. This results inan effective lubrication of the lower bearing 5, the interior of whichcommunicates with the upper part of the chamber 17.

By the rotation of the spindle also the fan device 39 is brought intorotation. This generates a certain overpressure in the intermediatechamber 13 and a certain underpressure in the upper chamber 11. Hereby,transportation of oil mist is accomplished from the lower chamber 17,through the openings 37, the channels 36 and the openings 38, to theupper chamber 11. Herefrom the oil mist is conducted through at leastthe channels 31 to the interior of the bearing 6 and further through thecentral passage 40 to the suction side of the fan device 39. Thisresults in an effective lubrication of the upper bearing 6.

Air and possibly remaining oil mist is forced from the intermediatechamber 13 through the gap 16 of the motor back to the lower chamber 17.Also oil deposited on surfaces inside the housing 4 runs back to the oilbath in the lower chamber 17.

Upon rotation of the centrifugal rotor 1 unbalance may arise, e.g. as aresult of separated solid particles being unevenly distributed in theseparation chamber of the centrifugal rotor. Such unbalance may resultin the spindle 3 being subjected to bending and/or the spindle 3 beingcaused to perform a rotational movement around and at a distance from anew rotational axis of the centrifugal rotor. Such movements of thespindle 3, or a part of the same, can occur due to the spring suspensionof the upper bearing 6. Furthermore, in accordance with the invention,the gap 16 between the stator 14 and the rotor 15 of the electric motoris so wide, that this also permits such movements. For avoiding damageto the electric motor due to mechanical contact between the stator 14and the rotor 15 upon too large movements of the spindle 3, it issuitable that limiting members (not shown) for such movements areincluded in the above described suspension device in the upper part ofthe housing 4.

The gap 20 between the spindle 3 and the rotor 15 is dimensioned in away so that the spindle 3 may bended somewhat without contacting therotor 15 below the connection between the spindle 3 and the sleeve 18.

According to the invention the gap 16 between the stator 14 and therotor 15 of the motor has an important purpose to serve also by forminga transport path for the oil mist being transported in a circuit bymeans of the fan device 39. Thereby, in addition to lubricating andcooling the bearings 5 and 6 the oil mist also cool the motor 12, bothits rotor and its stator. Thus, the oil mist continually removes heatfrom the motor during transport of the oil through the gap 16 andtransfers this heat during its passage through the channels 36 to thecooling fluid flowing through the jacket 32. The cooling fluidsimultaneously cools the outside of the stator of the motor being incontact with the inside of the housing 4. As earlier indicated, the fandevice 39 alternatively may be arranged so that oil mist circulates inthe reverse direction in the circuit described above, i.e. upwardsthrough the gap 16 and downwards through the channels 36 on the outsideof the frame.

1. A driving device for a centrifugal separator, the centrifugalseparator including: a centrifugal rotor rotatable about a substantiallyvertical rotational axis (R); a spindle that supports at one end thereofthe centrifugal rotor; a frame, rotatably supporting the spindle duringnormal operation of the centrifugal rotor by means of a first bearingand a second bearing, said first bearing being arranged between thecentrifugal rotor and said second bearing; said driving devicecomprising an electric motor arranged to drive the spindle and having astator non-rotatably connected to the frame, and a rotor supported bythe spindle between the two bearings; a spring device arranged to permitbut counteract by spring force, in an area axially between thecentrifugal rotor and the electric motor, radial movement of the firstbearing relative to the frame; a bearing support member supported by theframe and arranged to prevent substantial radial movement of said secondbearing; and wherein the stator of the motor is fixed to the frame andis immovable relative thereto, the rotor of the motor being radiallymovable relative to the stator together with the spindle, a gap betweenthe rotor and the stator of the motor being dimensioned to permit theradial movement of the rotor of the motor.
 2. A driving device accordingto claim 1, further comprising a lubricating device arranged forlubrication of said two bearings, the lubricating device having agenerating member for generating an oil mist in an oil chamber, thefirst bearing and the second bearing being arranged in a first bearingchamber and a second bearing chamber, respectively, through which oilpassages communicate with said oil chamber, and wherein the gap betweenthe rotor and the stator of the motor forms at least part of a flow pathfor oil axially through the motor.
 3. A driving device according toclaim 2, wherein the lubricating device comprises a fan device arrangedto transport oil mist in a circuit that includes the said gap.
 4. Adriving device according to claim 3, wherein the fan device is connectedto the spindle for rotation therewith.
 5. A driving device according toclaim 4, wherein the fan device is arranged between the first bearingchamber and an intermediate chamber in communication with the gap, thefan device being arranged to transport oil mist in one of the directionsbetween the first bearing chamber and the intermediate chamber.
 6. Adriving device according to claim 3, wherein the circuit includes thegap and at least one further passage connecting the said bearingchambers with each other.
 7. A driving device according to claim 6,wherein the passage is delimited between and outside of the frame and amember connected to the frame.
 8. A driving device according to claim 7,wherein the frame is surrounded by a jacket forming said member anddelimiting a space for through flow of a cooling medium in heattransferring contact with the frame.
 9. A driving device according toclaim 8, wherein the jacket is double-walled, an inner one of the jacketwalls delimiting the channels together with the frame.
 10. A drivingdevice according to claim 7, wherein the passage includes severalchannels evenly distributed around the spindle and delimited between theframe and the member.
 11. A driving device according to claim 1, whereinthe centrifugal rotor is supported at the upper end of the spindle. 12.A driving device according to claim 11, wherein the frame surrounds aspace in which the electric motor and a part of the spindle and also thetwo bearings are arranged, the frame being formed such that said spaceis closed from connection with the surrounding atmosphere below saidfirst bearing.
 13. A driving device according to claim 1, wherein thefirst bearing is arranged to take up substantially all axial forces tobe transferred between the spindle and the frame.
 14. A driving deviceaccording to claim 1, wherein the rotor of the motor is coupled at oneend of the spindle in such a way that it is radially immovable relativeto the spindle in an area adjacent a location where the spindle iscoupled to the motor rotor, the motor rotor being otherwise radiallymovable relative to the spindle.
 15. A driving device according to claim1, wherein rotor of the motor comprises a first part in the form of asubstantially cylindrical sleeve connected to the spindle, and a secondpart surrounding the sleeve and connected to an outside surface thereof.16. A driving device according to claim 1, wherein the rotor of themotor surrounds the spindle, a heat-insulating gap being formed betweenthe rotor and the spindle at least along a part of the rotor of themotor.